This invention pertains to a hydraulic oscillator wherein a vibratory member is brought into self-excited vibration inside an oil pressure chamber by means of oil pressure so as to generate alternating flow at oil pressure outlets by vibration thereof, said oscillator being effectively used as driving means for appropriate types of mechanisms and machinery.
Machines which function by oscillation or reciprocation, such as a pile drivers, perform the function by transmitting impulses from, for instance, a vertical reciprocating device to piles or the like. Such machines are never free from serious problems with respect to environmental destruction on account of their noise and vibration.
Customary machines which involve vibration, such as a pile driver, generally utilize the driving force of vibration by way of a rotating eccentric load driven by an electric motor. Because of the tremendous load imposed on bearings and the like, however, these machines can operate at rates of only about 20 CPS but not higher; in addition, it is extremely difficult to change the frequency and/or the impact of vibration during the operation.
In order to overcome such problems, there have been proposed several methods; and in one case, an eccentric load which permits the change of vibration during the operation is rotated by an oil pressure motor or the like so as to obtain the driving force of vibration. In another case, an eccentric load is reciprocated by the use of an electro-hydraulic servo valve, etc., in a cylinder. However, it is very difficult to obtain a more forceful vibration in the former case, while in the latter case the frequency characteristics become extremely inferior as the apparatus becomes larger in volume; also the increase in size makes the apparatus more expensive to fabricate and more complex in design, although the latter does permit a higher frequency.
In the past few years there has been a proposal for the solution of these problems in which a hydraulic oscillator is used which employs positively self-excited vibration of oil pressure known as a dynamic characteristic of oil pressure valves.
As an example of said hydraulic oscillator, there has been proposed a spool valve type self-excited oscillator. In this type of the oscillator, however, slight displacement of a spool in one direction is multiplied by transient axial force, and the spool stops its excursion at a position where the displacement balances with the force of inertia, viscous resistance and the restoration force of fluid, and thereafter the spool is moved in the opposite direction by the force of restoration of fluid. In this manner, the spool repeats the sequence of movement and continues to vibrate or reciprocate. However, the point at which the spool stops is not constant, but varies in accordance with the accuracy of component parts, temperature of oil, flow volume, etc., continuously. When the transient axial force is increased so as to improve the oscillation characteristics, the displacement increases correspondingly, and vibration becomes smaller in consequence until at last the vibration stops at the end of a stroke.
When the force of restoration of fluid is increased so as to increase the vibration, on the other hand, the oscillation characteristics becomes inferior, and the spool stops its vibration at a neutral position. It has been found that selection as well as maintenance of optimum operating conditions are almost impossible due to various factors such as force of inertia, viscous resistance and so forth.